For convenience, terminology adopted by the 3GPP (3rd Generation Partnership Project) will be used throughout detailed description of this specification e.g. User Equipment and UE. However the present invention should not be considered as being limited to application in systems implemented in accordance with 3GPP standards.
The Orthogonal Frequency Division Multiple Access (OFDMA) system divides the frequency domain and time domain and allocates a sub-channel to each user. Each sub-channel comprises a plurality of sub-carriers (frequency domain), and a plurality of time slots (time domain). The OFDMA system is based on a multiple access scheme capable of accommodating multiple users using limited frequency resources by performing resource allocation whilst taking into account both the time and frequency domains.
The OFDMA system is intended to support a flexible transmission bandwidth up to 20 MHz. However, User Equipment (UE) having a lesser capability must also be supported. The UE capability is defined as maximum reception bandwidth that UE can support. FIG. 1 is a representation 10 of an exemplary set of camp bands in an OFDMA system having a 20 MHz transmission bandwidth and supporting different UE capabilities. It can be seen from this figure that within the 20 MHz transmission bandwidth, it is possible to have one camp band for 20 MHz UE capability and multiple camp bands for 5, 10 and 15 MHz UE capability. Three camp bands 14, 16 and 18 are illustrated for 15 MHz UE, three camp bands 20, 22 and 24 are illustrated for 10 MHz UE, and seven camp bands 26 to 38 are represented for 5 MHz UE.
In such a system, the various UE initially camps at a central frequency in order to receive information from the broadcast channel (BCH), synchronization channel (SYNCH) and paging channel (PCH) within the transmission bandwidth 40. Once the UE has performed cell search procedure, time and frequency correction and synchronization with a base station, the UE remains idle until information is received from within the bandwidth 40 to instruct the UE to move to one of the multiple camp bands shown in FIG. 1. Once there, the UE monitors the shared control channel (SCCH) and determines when information subsequently received on the shared data channel is intended for that UE.
Information from the transport shared control channel (SCCH) for each UE is mapped to a physical shared control channel (PSCCH) for transmission to each UE. In the OFDMA system, it is intended that any UE shall only receive PSCCHs in a camp band corresponding to the reception bandwidth capacity of that UE. Moreover, it is intended that transmissions to UEs having different reception bandwidth capacities can be scheduled within a same Transmission Time Interval (TTI). The structure of the SCCH and PSCCH should also be such that any UE can apply the same processing to receive the shared control channel regardless of the position of the UE's camp band within the transmission band. Finally, all available SCCHs in the system can be grouped into sets. Each SCCH set may contains multiple SCCHs. Each UE is required to monitor one or more SCCH sets depending upon its capability.